Low Friction Systems and Devices

ABSTRACT

Disclosed herein are compositions and systems having a low coefficient of friction. The low friction system comprises a first surface and a second surface, where the first surface comprises (i) a polycarbonate and a first additive, or (ii) a polybutylene terephthalate and a second additive; and the second surface comprises a polyoxymethylene and a third additive. The low friction compositions and systems are valuable for producing devices, such as medical devices.

FIELD OF THE INVENTION

The present invention relates to low friction systems that are used formaking sliding components, and further for producing devices. Theinvention also relates to compositions useful for producing such lowfriction systems and devices.

BACKGROUND OF THE INVENTION

When two materials slide against each other, it is often desirable tohave a smooth contact between the surfaces of the materials so to reducefriction at the contact area. For a given pair of sliding surfaces, themagnitude of friction is generally given by the coefficient of friction.A lowering of the coefficient of friction generally leads to improvedwear and reduced squeaking noises.

An important area of application where smoothly sliding materials areneeded is in drug injection systems, which are commonly used to delivertherapeutic agents. Pen injectors constitute one class of drug injectionsystems. Pen injection components are commonly made of plasticmaterials, such as thermoplastics. The components are generally producedby injection moulding techniques. Pen injectors are widely used fordelivering or injecting therapeutic agents into the body, example, ahuman body. Surfaces of a pen injection system that are in contact witheach other slide during injection of the therapeutic agent into thehuman body. This leads to friction between the surfaces of thecomponents that are in contact during the sliding motion. For example,the outer surface of a piston experiences sliding friction when itslides against a cylindrical tube of a pen injection system. The forcewith which a therapeutic agent is injected into a human body through apen injection system is termed as dose force. One of the factors thatdetermines the dose force in the pen injector is the friction betweencomponents of the pen injector that slide against each other. Therefore,if friction can be reduced, the dose force can also be reducedadvantageously, thereby leading to a smoother operation and longer useof the injection system.

The known pen injector components exhibit a relatively high coefficientof friction when they slide against each other. Further, the componentsmanufactured by commonly known techniques, such as injection moulding,require extensive running in, external lubrication, or both to obtain aninstantaneous low coefficient of friction between them.

Therefore, there is a need for a system having components having a lowcoefficient of friction, that is, a coefficient of friction of less than0.06 when measured using a contact pressure of 3.0 MPa (megapascals) anda sliding speed of 0.02 meters per second. Further, there is a need formethods for producing a low friction system that exhibits a lowcoefficient of friction of less than or equal to 0.06, withoutsubjecting the components to the extra steps of exhaustive running-in,external lubrication, or both. Furthermore, there is a need for a systemwherein after additional external lubrication of one or both components'surface(s), the frictional force is not further reduced.

SUMMARY OF THE INVENTION

The invention provides low friction systems and devices havingcomponents that exhibit a low coefficient of friction when there isrelative motion between the components.

In one aspect, the invention provides a system comprising a firstsurface comprising: (i) a polycarbonate and a first additive, or (ii) apolybutylene terephthalate and a second additive; and a second surfacecomprising a polyoxymethylene and a third additive.

In another aspect, the invention provides a system comprising devicecomprising a first component in surface contact with a second component,the first component comprising: (i) a polycarbonate comprising a firstadditive, or (ii) a polybutylene terephthalate comprising a secondadditive; and the second component comprising a polyoxymethylenecomprising a third additive.

In still another aspect, a method for producing a device comprises:forming a first moulding composition comprising a polycarbonate and afirst additive, or a polybutylene terephthalate and a second additive;forming a second moulding composition comprising a polyoxymethylene anda third additive; and moulding the first and second mouldingcompositions.

In still yet another aspect, the invention provides a compositioncomprising: (i) a polycarbonate and a first additive, or a polybutyleneterephthalate and a second additive, which form a first component; and(ii) a polyoxymethylene and a third additive, which form a secondcomponent; wherein the first and the second components upon mutualcontact form a low friction system.

The systems and devices disclosed herein have a low coefficient offriction, that is a coefficient of friction of less than or equal to0.06, when measured using a contact pressure of 3.0 MPa and a slidingspeed of 0.02 meters per second.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary low friction system comprising a firstand a second component, which press and slide circularly against eachother, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides systems and devices having two or more surfacescomprising certain combinations of polymer materials. Such surfaces uponcontact and relative sliding motion have a low coefficient of friction,that is a coefficient of friction of less than or equal to 0.06, whenmeasured using a contact pressure of 3.0 MPa and a sliding speed of 0.02meters per second.

In one aspect of the invention is disclosed a system comprising a firstsurface comprising: (i) a polycarbonate and a first additive, or (ii) apolybutylene terephthalate and a second additive; and a second surfacecomprising a polyoxymethylene and a third additive.

In another embodiment, the present invention provides a systemcomprising: a first surface comprising a polycarbonate and a firstadditive; and a second surface comprising a polyoxymethylene and a thirdadditive. In still another embodiment, the present invention provides asystem comprising: a first surface comprising a polybutyleneterephthalate and a second additive; and a second surface comprising apolyoxymethylene and a third additive.

The first additive is preferably a silicone. Silicones, also sometimesreferred to as polysiloxanes, polyorganosiloxanes, or organosilicones,are polymers consisting of a silicon-oxygen backbone (—Si—O—Si—O—Si—O—)and substituted on the silicon atoms with organic groups, such as alkylgroups and/or aryl groups. Silicones are odorless, colorless,water-resistant, chemical-resistant, oxidation-resistant and stable athigh temperatures, and do not conduct electricity. Silicones areavailable in various structural variations and in various molecularweights. By way of an example, silicones having methyl groups as thesubstituents, commonly known as polydimethylsiloxanes are readilyavailable in a range of molecular weights and viscosity ranges. In anembodiment, silicone oils can be used as the first additive with thepolycarbonate. The silicone oil and the polycarbonate are independentlyin a relative weight ratio from 0.001 to 0.05.

The third additive for use with the polyoxymethylene is preferably alsoa silicone as described above. In an embodiment, the first and the thirdadditives can be the same silicone. In another embodiment, the first andthe third additives can be different silicones. In still otherembodiments, different silicone oils having the same organicsubstituents on the silicon, but different viscosity ranges can also beused.

In an embodiment, the first, second, and the third additives can all bethe same silicone. In another embodiment, any two of the first, second,and the third additives can be the same silicone. In still anotherembodiment, the first, second, and the third additive can all bedifferent silicones having the same organic substituents on the siliconatoms, but different viscosities or molecular weights. Other possiblevariations of combinations of molecular weight, substitution patterns,and viscosities based on the wide range of silicones known in the artare also possible.

The first surface comprising the polycarbonate and the first additivemay further comprise a fourth additive. In another embodiment, thesecond surface comprising the polyoxymethylene and the third additivemay further comprise a fifth additive. The fourth and the fifth additivemay each independently comprise an ethylene polymer a fluorinatedethylene polymer, or combinations of the ethylene polymer and thefluorinated ethylene polymer. Thus, the fourth and the fifth additivesmay each be an ethylene polymer in an embodiment, an ethylene polymerand a fluorinated ethylene polymer, respectively, in another embodiment;and each a fluorinated ethylene polymer in still another embodiment.Other possible variations of these polymers can also be used. Moreover,the ethylene polymers and the fluorinated ethylene polymers can have thesame molecular weight, or different molecular weights. Suitable ethylenepolymers include ethylene homopolymers and copolymers. In an embodiment,polyethylene, abbreviated as PE is a suitable ethylene polymer for usewith the polycarbonate and the first additive for the first surface.Suitable examples of fluorinated ethylene polymers includepolytetrafluorethylene, abbreviated as PTFE. In another embodiment, asystem comprising a first and a second surface is disclosed wherein thefirst surface comprises a polycarbonate, a silicone oil as the firstadditive, and a polyethylene as the fourth additive; or a polybutyleneterephthalate and a second additive; and the second surface comprises apolyoxymethylene, a silicone oil as the first additive, and apolyethylene as the fifth additive.

In an embodiment, the ethylene polymer and the polyoxymethylene, and theethylene polymer and the polycarbonate may be present independently in aweight ratio from 0.01 to 0.99. In another embodiment, the fluorinatedethylene polymer and the polyoxymethylene, and the fluorinated ethylenepolymer and the polycarbonate may be present independently in a weighratio from 0.01 to 0.99.

The polycarbonate for forming the first surface may, in an embodiment,include any of the known polycarbonate homopolymers and copolymers.Polycarbonates are commercially valuable thermoplastic polymers whichare generally produced using one or more aromatic bisphenols.Polycarbonates homopolymers and copolymers prepared using bisphenol A asa monomer or a comonomer are widely available, and may be usedadvantageously for forming the low friction systems of the presentinvention. In a particular embodiment, the polycarbonate forming thefirst surface is bisphenol A polycarbonate. Polycarbonates are availableunder various trade names, such as ALCOM®, ALFACARB®; ANJALON®, APEC®,ASTALON®, AXXISPC®, AZLOY®, BARLO®, BAYBLEND®, BEETLE® CALIBRE®,DECARGLAS®, ECOCARB®, IUPON®, NAXELL®, POLYGAL®, SERACARB®, TEKULON®,ULTRATUF® and ZELUX®. Commercial manufacturers of polycarbonate includeGE Plastics, Dow, BASF, Mitsubishi, Bayer, RTP Company, and TeijinChemicals.

The polybutylene terephthalate which is suitable for use as analternative material for the first surface may in principle be any typeof a homopolymer or a copolymer. Any of the polybutylene terephthalatesknown in the art may be used. Polybutylene terephthalate is generallyproduced commercially by reacting 1,4-butylene glycol with terephthalicacid. Polybutylene terephthalate copolymers comprising structural unitsderived from other aliphatic diol comonomers, such as for example,ethylene glycol and 1,3-propanediol may also be used. Commercialmanufacturers of polybutylene terephthalate include GE Plastics, Toray,BASF, and Ticona. Some examples of commercially available grades ofpolybutylene terephthalate include ACESTER®, VALOX®, ALCOM®, ALFATER®,ANJADUR®, ARNITE®, AZDEL®, AZMET®, BADADUR®, BAYFOL®, BEETLE®,BERGADUE®, BST®, CELANEX®, CRASTIN®, DAFNELOV®, DENITER®, DURANEX®,DURLEX®, DURMAX®, DYNACOM®, EKTAR®, ENDURAN®, ENPLAC®, ENSITEP®,GRILPET®, HAUZER®, HILOY®, HYNSIN®, KAIFA®, KOPLA®, LATER®, LEMAPET®,LUMAX®, LUPDX®, LUPOY®, LUTREL®, LUVOCOM®, MAXNITE®, NEVIESTER®,NIBLAN®, NOVADURAN®, ORGATER®, PALDUR®, PERLOX®, PERMASTAT®, PETLON®,PIBITER®, PLANAC®, POCAN®, POLYSHINE®, RADIFLAM®, RADITER®, RYNITE®,SCHULADUR®, SEGREGATE®, SERATEC®, SHINITE®, SPESIN®, TARALOX®, TECADUR®,TECDUR®, TECHSTER®, TISMO POTICON®, TOPEX®, TRIBIT®, TUFPET®, TYNEP®,ULTRADUR®, VAMPTER®, VANDAR®, VESTODUR®, VEXEL®, and WHISTATT®.

The polyoxymethylene (abbreviated herein as “POM”) is also referred tocommonly by other names, such as polyacetal and acetal polymer. In POMthe repeating structural unit in the polymer chain is the oxymethylenegroup (—OCH2—). In an embodiment, polyoxymethylene copolymers may alsobe used. For example, a copolymer obtained by using a comonomer havingone or more glycidyloxy groups may be used. POMs are available undervarious trade names such as HOSTAFORM® AMCEL®, CELCON®, DELRIN®,KEPITAL®, ENSITAL®, KOPLA®, PALFORM®, TEPCON® and ULTRAFORM®. Suppliersof POM include Ashley Polymers, DuPont company, RTP Company, and ShumanPlastics, Inc.

The fluorinated ethylene polymer may be any homopolymer or copolymerproduced from an ethylene monomer having at least one fluorine atom. Thefluorine atom may be a vinylic fluorine atom or form part of afluoroalkyl group, such as a monofluoromethyl, difluoromethyl,trifluoromethyl, and perfluoroalkyl. For example, apoly(perfluoroalkylene ether) may be used. Mixtures of variousfluorinated ethylene polymers may also be used. Polytetrafluoroethylene(commonly known as “PTFE”, also known as Teflon®) may also be used as afluorinated ethylene polymer. It is generally obtained by polymerizingtetrafluoroethylene. PTFE is generally an inert polymer under normalconditions of use.

The ethylene polymer includes all types of polymers other than thefluorinated ethylene polymers described hereinabove. Suitable ethylenepolymers include homopolymers and copolymers produced using ethylene asa monomer or a comonomer, respectively. Polyethylenes with or withoutchain branches may be used as a suitable fourth or fifth additive. Thuspolyethylene homopolymers and copolymers known in the art may be used.Polyethylenes of varying densities are generally obtained by controllingthe molecular weight and density of branching, such as long chainbranching along the polymer backbone. Suitable ethylene polymers includeultra-high molecular weight polyethylenes, high density polyethylenes,high density cross-linked polyethylenes, cross-linked polyethylenes, lowdensity polyethylenes, linear low density polyethylenes, and very lowdensity polyethylenes. Polyethylenes having a density of greater than orequal to 0.94 grams per cubic centimeter are generally considered ashigh density polyethylenes. Low density polyethylenes are generallymaterials having a density of 0.91-0.94 grams per cubic centimeter.Linear low density polyethylenes are generally materials having adensity of 0.915-0.925 grams per cubic centimeter. Very low densitypolyethylenes are generally materials having a density of 0.88-0.915grams per cubic centimeter.

In an embodiment, the ethylene polymer and the polycarbonate, and theethylene polymer and the POM are independently present in a relativeweight ratio from 0.01 to 0.99. In another embodiment, the fluorinatedethylene polymer and the polyoxymethylene, and the ethylene polymer andthe polycarbonate are independently in a relative weight ratio from 0.01to 0.99.

The materials described hereinabove provide for a composition forforming a low friction system having a low coefficient of friction thatis less than or equal to 0.06. In an embodiment, a composition isprovided which comprises: (i) a polycarbonate and a first additive, or apolybutylene terephthalate and a second additive, which form a firstcomponent; and (ii) a polyoxymethylene and a third additive which form asecond component; wherein the first and the second components uponmutual contact form a low friction system. In another embodiment, thepresent invention provides a composition comprising a polycarbonate anda first additive, which form a first component; and a polyoxymethyleneand a third additive, which form a second component; wherein the firstand the second components upon contact form a low friction system. Instill another embodiment, the present invention provides a compositioncomprising a polybutylene terephthalate and a second additive, whichform a first component; and a polyoxymethylene and a third additive,which form a second component; wherein the first and the secondcomponents upon contact form a low friction system.

The materials and compositions described hereinabove are applicable forforming low friction systems and devices. In an embodiment, such adevice comprises a first component in surface contact with a secondcomponent, wherein the first component comprises: (i) a polycarbonateand a first additive, or (ii) a polybutylene terephthalate and a secondadditive; and the second component comprises a POM comprising a thirdadditive. In another embodiment, the device comprises a first componentin surface contact with a second component, wherein the first componentcomprises a polycarbonate and a first additive; and the second componentcomprises a POM and a third additive. In still another embodiment, thedevice comprises a first component in surface contact with a secondcomponent, wherein the first component comprises a polybutyleneterephthalate and a second additive; and the second component comprisesa POM and a third additive.

The first and the second surfaces of the systems and the devices can bein relative motion in various ways. Thus the first surface may bestationary with respect to the second surface in an embodiment; and thesecond surface may be stationary with respect to the first surface inanother embodiment. In still other embodiments, the first and the secondsurfaces may both be moving in the same direction at same or differentspeeds; the first and the second surfaces may both be moving in oppositedirections at same or different speeds. When the surfaces slide relativeto each other while maintaining contact, friction is produced at thecontact zone. In accordance with an exemplary embodiment of the presentinvention, the contact zone has a coefficient of friction less than orequal to 0.06 when the two surfaces are in relative motion with respectto each other. FIG. 1 illustrates an exemplary system 100 having a firstsurface 102 that slides against a second surface 104, in accordance withan embodiment of the invention. Non-limiting examples of chemicalcompositions that can be used for the first surface 102 and the secondsurface 104 to form low friction systems having a coefficient of lessthan or equal to 0.06 are shown in Table 1, which is discussed furtherbelow herein.

The low friction systems are valuable for producing devices havingsliding components that can operate more smoothly with less wear, suchas devices that are used in healthcare and therapeutic applications. Noexternal lubrication is needed, which leads to lower contamination ofthe materials with which the sliding surfaces come in contact. In anembodiment, injection systems or injection devices having a lower dosingforce as compared to injection systems currently known in the art can beproduced. Pen injectors having a lower dosing force for injecting drugsor medicaments, such as insulin can be produced. Other potentialapplications include use for making hinges for liquid crystal displaydevices, and pump bearings.

The low friction devices may be produced by a method which comprises:forming a first moulding composition comprising a polycarbonate and afirst additive and optionally a fourth additive, or a polybutyleneterephthalate and a second additive and optionally a fifth additive;forming a second moulding composition comprising a POM and a thirdadditive; and moulding the first and second moulding compositions. Anyof the various techniques known in the art for moulding plasticmaterials may be used. The invention is further illustrated with thefollowing Examples.

EXAMPLES

For testing purposes, the first and second moulding compositions may bemoulded to form discs or plates. Various amounts of the base polymer andthe other ingredients for preparing the moulding compositions and themoulded specimens are shown in Table 1. The discs (test specimens),consisting of a lower rotary polymer specimen and an upper stationarypolymer specimen were mounted on a testing device used for measuring thecoefficient of friction. The tests were carried out by adapting theprocedure described in ASTM standard D-3702 (re-approved in 2004) testmethod to those used for testing medical devices, by employing a contactpressure between the test specimens of 3 MPa and a sliding speed of 0.02meters per second. The results are shown in Table 1, which also showsthe chemical compositions of the first component 102 and the secondcomponent 104, and the measured coefficient of friction for each pair ofcomponents. In Table 1, the abbreviations mean the following:“PC”—polycarbonate; “PBT”—polybutylene terephthalate; “PE”—polyethylene;“COE”—coefficient of friction; “PC-Si”—a polycarbonate-siloxane blockcopolymer, commercially available as EXL 1112 grade; and“POM”—polyoxymethylene; “E” stands for Example; and “CE” stands forComparative Example.

TABLE 1 Weight Percent of Weight Percent of Ingredients in Ingredientsin First Component 102 Second Component 104 Sil- Sil- Expt Base iconeBase icone No. Polymer oil PTFE PE Polymer oil PTFE PE COE E-1 PC 2 18 0POM 2 18 0 0.04 E-2 PC 2 0 0 POM 2 5 0 0.06 E-3 PC 2 0 0 POM 2 10 0 0.06E-4 PC 2 0 0 POM 2 18 0 0.06 E-5 PC 2 5 0 POM 2 10 0 0.06 E-6 PC 2 5 0POM 2 18 0 0.06 E-7 PC 2 10 0 POM 2 10 0 0.06 E-8 PC 2 10 0 POM 2 18 00.06 E-9 PC 2 0 0 POM 2 0 10 0.05 E-10 PC 2 0 2 POM 2 0 10 0.05 E-11 PC2 0 5 POM 2 0 10 0.05 E-12 PC 2 0 7 POM 2 0 10 0.05 E-13 PC 2 0 40 POM 20 5 0.06 E-14 PBT 2 0 0 POM 2 0 5 0.05 E-15 PBT 2 0 0 POM 0 0 0 0.04E-16 PBT 2 0 0 POM 2 0 0 0.06 CE-1 PC-Si 0 0 0 POM 0 0 0 0.16 CE-2 PBT 00 0 POM 0 0 0 0.14

Inspection of the data in Table 1 shows that the various polymercompositions as shown can be used for producing low friction systemshaving a coefficient of friction of less than or equal to 0.06. Further,the low friction is achieved almost instantaneously with very littlerunning in of the moulded components

The use of any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention. Any references cited herein are incorporated in theirentirety.

This invention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. While the preferred embodiments of the invention have beenillustrated and described, it will be clear that the invention is notlimited to these embodiments only. Numerous modifications, changes,variations, substitutions and equivalents will be apparent to thoseskilled in the art without departing from the spirit and scope of theinvention, as described in the claims.

1.-15. (canceled)
 16. A method for producing a device, comprising:forming a first moulding composition comprising a polycarbonate and afirst additive and optionally a fourth additive, or a polybutyleneterephthalate and a second additive and optionally a fifth additive;forming a second moulding composition comprising a polyoxymethylene anda third additive; and moulding the first and second mouldingcompositions.
 17. A composition, comprising: (i) a polycarbonate and afirst additive, or a polybutylene terephthalate and a second additive,which form a first component; and (ii) a polyoxymethylene and a thirdadditive, which form a second component; wherein the first and thesecond components upon mutual contact form a low friction system.